The heparin cap refers to a device used in medical settings. It is a small cap that is attached to the end of an intravenous (IV) catheter or other vascular access device. The cap contains a small amount of heparin, an anticoagulant (blood thinner), which helps prevent blood clots from forming in the catheter and tubing.

The purpose of the heparin cap is to maintain patency (openness) of the catheter and prevent it from becoming blocked by blood clots. It is commonly used in situations where an IV catheter is not in constant use but needs to remain open for intermittent medication administration or blood draws.